The **watt-hour** is a unit of energy equal to one watt of output for an hour.^{[1]} It is equal to 3,600 joules. While the watt is the SI unit of power, electrical power consumption is usually measured in Kilowatt-hours for a household. Electrical energy generated by a power plant is often measured in TWh (over the course of a year). This idea is closely related to the watt-year (or the more commonly used GWy).

A kilowatt-hour is a unit of energy equal to outputting one thousand watts for one hour. It is equal to 3,600,000 Joules. The kilowatt hour is the unit of measurement for a residential power bill, and we usually use kilowatt hours for personal energy use. It is abbreviated kWh.

A terawatt-hour is a unit of energy equal to outputting one trillion watts for one hour. It is equal to 3.6x10^{15} Joules. This value is large enough to express annual electricity generation for entire countries, and is often used when describing major energy production or consumption.

To read more about the watt-hour, click here.

To read more about the kilowatt-hour, click here

- ↑ UCS,
*How is Electricity Measured*[Online], Available: http://www.ucsusa.org/clean_energy/our-energy-choices/how-is-electricity-measured.html#.VP0MnPRDuT8